Disk drive and tape drive technologies are well known areas of the storage medium technology. However, the storage medium technology has not experienced a demand for substantial performance improvement until the more recent market demand for computers to handle multimedia. With the onset of multimedia applications, there is now a substantial performance improvement needed of disk drive and tape drive technology to satisfy the memory intensive requirements of the various multimedia applications, and to also support the increased access bandwidth required by the faster processors being developed for multimedia processing.
The density of the stored memory in a typical disk depends on how close the data can be written into disk. For an inductive head writer, the write current rise and fall times directly affect the density of a magnetic storage medium. The faster the write current rise and fall time, the faster the change of the magnetic flux, and consequently more bits per inch can be stored in the media. The rate of change of current in an inductor is calculated as shown in the following standard equations: EQU V=L.sub.h (di/dt) (1) EQU di/dt=V/L.sub.h ( 2)
where
V=the voltage swing across the thin film head PA1 L.sub.h =the head inductance PA1 di/dt=the rate of change of the write current
As shown in the above equation (2) the write current rate (di/dt), across an inductive head is directly proportional to the voltage swing across the thin film head (V), and accordingly a fast write current rate (di/dt), can be achieved by increasing voltage swing V across the head inductance, or by lowering the head inductance (L.sub.h).
There is, however, a fundamental limit as to how fast current can change in an inductive device due to an inherent capacitor in the inductive head (C.sub.h), along with the head inductance (L.sub.h). The total capacitance (C.sub.tot) is a combination of head capacitor (C.sub.h), the parasitic capacitors, as well as the write driver capacitor (C.sub.d). The fastest write current rise and fall time is limited to the resonance frequency of the (L.sub.h) and (C.sub.tot), more specifically the resonance frequency is proportional to the 1/sqrt(L.sub.h)(C.sub.tot)!. At resonance frequency, overshoot and undershoot ringing will typically occur. Too much ringing results in prolonging the settling time of the write current, and consequently affecting the performance of the write driver. To remove ringing, damping resistor (R.sub.d), is typically placed across the inductor head. Unfortunately, the damping resistor operates to slow down the write current rise and fall time by reducing the amount of current through the head inductor (L.sub.h), as shown by the following equation for calculating the write current through the inductive head: EQU I.sub.w =I/1+R.sub.head /R.sub.d ! (3)
The lower the damping resistor, R.sub.d, the smaller the effective write current. Consequently, there is therefore a need for write drivers that can provide rail to rail voltage swing very quickly even with a damping resistor attached. More specifically, there is a need for write drivers that have faster write current rise and fall times to provide greater storage density to meet the demand for higher density and faster disk drives.